In the past, if solar energy concentrating systems were used on top of buildings or roofed structures to gather radiant solar energy, then one could select from two options. The first option was simply to take a solar energy concentrating system suitable for use on the ground and mount it up on top of a roofed structure. While such an approach did gather radiant solar energy, it also required that the roof support a substantially greater weight. This add-on approach resulted in substantially higher capital costs. Moreover, once the system was atop the roofed structure, inevitably the underlying roof would need repair. The presence of the system atop the roof in a non-integrated fashion increased the ease and cost of making roof repairs.
The second option was to make a substantial portion of the roof into a solar energy concentrating reflector. An example of this unitary reflector approach can be found in U.S. Pat. No. 3,994,435 to Barr. While Barr no longer had the disadvantage of added supporting structure as in the add-on approach, Barr had to make compromises in gathering the radiant solar energy. The semi-cylindrical reflector and fixed collector did not collect as much solar energy as ground-based units with better geometries. Also, Barr required that the underlying building have a shape similar to the reflector, and thus, the ends of the Bart building had to swoop arcuately upwards, mimicking the reflector arc. Such a requirement had obvious disadvantages in being used on the numerous flat roofed buildings and roofed structures which are used for commercial or industrial purposes.